As others have said, if you get a good quality filter, it'll be very hard to tell the difference in the final image- even pixel-peeping with a high quality lens/camera. That's assuming the scene doesn't have a flare problem; a filter can only exacerbate any flare, so it's essential to choose one which has good quality multicoating. You can get an idea of how various filters perform by looking here:

Finally, beware of counterfeit filters: it's very easy for cheap filters to masquerade as the decent stuff, so you MUST buy from a reputable dealer. And even then, it's probably worth doing a few test shots to confirm you're getting zero negative effect on image quality. (If you get a dodgy filter, it'll usually be all too apparent in the final image.)